In recent years, transparent synthetic resins having a high refractive index have found increasing applications as optical plastic materials replacing inorganic optical materials because of their light weight and good impact strength, moldability or processability and dyeability.
Plastics used in the preparation of optical devices must have properties suitable for the intended purpose. These materials should, inter alia, be transparent, non-yellowing, and have a suitable refractive index. In general, the higher the refractive index polymer allows for a thinner more lightweight lens, as well as an improved physical appearance. A refractive index of 1.5 or greater is desired, and higher refractive index plastics, e.g., 1.6, 1.7, 1.8, or more, are preferred.
Many different types of plastics are used to manufacture optical lenses, and these plastics are well-known in the art.
Further, some specific sulfur-containing, monomers have been described as useful for producing optical lenses with desirable refractive indices. For example, U.S. Pat. No. 4,810,812 discloses thiolcarboxylic acid esters which are said to have a high refractive index and suitable transparency. Additionally, 2,5-dimercaptomethyl 1,4-dithian of formula:
is disclosed in U.S. Pat. No. 5,403,938 and is said to be suitable for use in optical materials with high heat resistance and excellent mechanical properties as well as excellent optical properties.
An unsubstituted 4,4 spirotetrathiocarbamate compound having the formula:
has been reported. The synthesis of the [4.4]STOC (above) is reported by D'Amico et al. in U.S. Pat. No. 3,525,752 and D'Amico in U.S. Pat. No. 3,652,256; and by D. L. Coffen, J. Heterocycl. Chem., 7:201, 1970. Compounds of this type or partial or full oxa derivatives have been investigated with regard to expansion polymerization. T. Endo and T. Tanaka, Macromolecules, 21:2314, 1988.
A compound of formula:
has also been reported in M. Barbero, et al., J. Chem Soc., Perkin Trans 1, 3:289-94, 1996. The paper is concerned only with the biological activity of SOTOC precursors and derivatives.
There are also reports of polymerizing a 5,5 spirotetrathiocarbamate as shown below:
(See J. J. D'Amico et al. in U.S. Pat. No. 3,525,752 and D'Amico in U.S. Pat. No. 3,652,256; and D. L. Coffen, J. Heterocycl. Chem., 7:201, 1970.)
U.S. Patent Application Publication 2002/0061995 discloses acrylic ester compounds of the general formula:
with specific substituents and polymerizable substituents bonded thereto. These compounds are said to be suitable resins for optical components having, inter alia, a high refractive index.
Despite the availability of a variety of optical polymers, new polymers with a high refractive index or other improved features are desirable.